'The group of men were standing' or 'the group of men was standing'?

Since all of the men are doing the same thing at the same time, the subject "group" is singular. This being so, the proper phrase is "The group of men was standing."

check my link for extra reading on the matter.

The subject of the sentence is "group". "Of men" is a prepositional phrase. Therefore, the verb must agree with the subject "group".

So -- the group WAS standing.

the group was standing

the men were standing

the GROUP (of men) was standing

You only have 1 group, it's singular.

It should be "was".

The group was, the groups were.

Most people tend to want to use were because of the plural (of men) that follows group, but just because it sounds and feels right (even to me), it doesn't mean it IS right.

the group of men were standing

'The group of men were standing'

It's were standing. The phrase group of men is plural.

The group WAS

the verb refers to GROUP - not men

That would be were

were